Various display devices characterized by its thin and flat structure such as a liquid-crystal display and a plasma display are prevailing widely as a display device in place of a cathode-ray tube. Also, a display using an organic EL expected to be a main stream of the next-generation display is being studied. Since the organic EL converts electricity into light using electroluminescence, it hardly generates heat and uses less power. Also, it has a characteristic that a sharp image can be displayed regardless of the viewing angle, unlike the liquid-crystal display.
FIGS. 9(a) and (b) are a sectional view and a corresponding circuit diagram of a light-emitting element comprising a light-emitting region using a conventional organic EL and SIT for driving when formed on a rigid substrate. On a glass substrate 100, a source region 101, a channel region 102, a light-emitting region 104 and a drain region 105 are sequentially laminated and formed. As the source region 101, a transparent electrode material such as ITO is used. As a material for the light-emitting region 104, an inorganic material such as ZnS and SrS, a low molecular organic EL such as Alq3 and NPB or a high molecular organic EL such as PPV and poly (3-alkylthiophene) is used. The SIT for driving is comprised by the source region 101, a semiconductor region 102 made of a P-type conductive polymer, a gate electrode 103 made of an N-type conductive polymer formed in the comb-tooth state and the drain region 105 in parallel with the source region 101 and the light-emitting region 104 within the semiconductor region 102. For example, the source region 101 is set to grounding potential, a negative bias voltage is applied to the drain region 105 and a positive control voltage is applied to the gate electrode 103. A positive hole injected from the source region 101 is re-bonded with an electron injected from the drain region 105 within the light-emitting region 104 to cause the light-emitting region 104 to emit light. The light-emitting intensity is controlled by the control voltage applied to the gate electrode 103.
FIG. 10 shows a sectional view of the light-emitting element comprised by the light-emitting region using a conventional organic EL and SIT for driving when formed on a flexible substrate. A source region 107, a semiconductor region 108, a light-emitting region 110 and a drain region 111 are sequentially laminated and formed on a plastic substrate 106. Also, a gate electrode 109 is formed in the comb-tooth state within the semiconductor region 108. In the conventional light-emitting element shown in FIG. 10, as with the conventional light-emitting element shown in FIG. 9, when the positive hole injected from the source region 107 and the electron injected from the drain region 111 are re-bonded within the light-emitting region 110, the light-emitting region 110 emits light. The light-emitting intensity of the light-emitting layer 110 is controlled by control voltage applied to the gate electrode 109.
As a method for driving control to display an image or to control illumination by arranging the light-emitting elements in the array state, a passive matrix method with a driving circuit provided outside and an active matrix method in which each of the light-emitting elements has a driving element are known. The active matrix method has the structure of the light-emitting element more complicated than the passive matrix method but is characterized by ability to be driven with a lower voltage, the life of light-emitting element is longer with lower power consumption and an external driving circuit is not needed.
FIG. 20 is a sectional view of an organic EL light-emitting element with a conventional SIT as its driving element. The conventional light-emitting element shown in FIG. 20 is comprised by a drain electrode 1202, a semiconductor layer 1204, a gate electrode 1203, a light-emitting layer 1205 and a source electrode 1206 sequentially laminated and formed on a glass substrate 1201. When a negative bias voltage is applied to the drain electrode 1202, an electron is injected from the source electrode 1206, an electron is injected from the source electrode 1206, a positive hole is injected from the drain electrode 1202, the injected electron and positive hole are re-bonded in the light-emitting layer 1205 and the light-emitting layer 1205 emits light. The light-emitting intensity is controlled by controlling the injecting amount of the positive hole through positive control voltage applied to the gate electrode 1203.
FIG. 21 is a sectional view of an organic EL light-emitting element having a control part in the conventional MOS structure. A cathode 1219 is arranged above a light-emitting layer 1220 with an anode 1218 under it, and gate electrodes 1214, 1215 are arranged on sides through gate insulating films 1216, 1217. When a negative bias voltage is applied to a cathode 219 and an anode 218, a positive hole is injected from the anode 218, an electron is injected from the cathode 1219, the injected electron and positive hole are bonded together again in the light-emitting layer 1220, and the light-emitting layer 1220 emits light. When a negative control voltage is applied to the gate electrode 1214 and a positive control voltage to the gate electrode 1215, a part of the electrons injected into the light-emitting layer 1220 are captured by the gate insulating film 1217, and a part of the injected positive holes are captured by the gate insulating film 1216 so that the number of the positive holes and electrons re-bonded in the light-emitting layer 1220 is reduced and the light-emitting intensity can be controlled.
In the conventional light-emitting element with SIT as the driving element shown in FIG. 20, the comb-tooth state gate electrode 1203 is formed by printing or deposition of a conductive organic film, and an interval L3 of the gate electrode 1203 can not be fully reduced. And since the controllability of the injected positive holes is low, it was necessary to apply a relatively high voltage to drive the light-emitting element.
On the other hand, with the conventional light-emitting element having a control part in the MOS structure shown in FIG. 21, the channel length, which is the interval between the cathode 1219 and the anode 1218 depends on the film thickness T2 of the light-emitting layer, and the channel length can be made not more than 1 μm and the light-emitting element can be made to emit light with a low voltage without using a fine process and with. However, it is necessary to form an insulating film on the side wall of the light-emitting layer and apply positive and negative control voltages to the gate electrodes formed on both the side faces, which led to a problem that manufacturing processes and control method are made complicated.